behind in payment on my commercial building bank threatening ,i have a buyer ,how long do i have before bank sell the bulding

Once the lender files a notice of default, then there is a 90 day period before the bank can file a notice of trustee sale, after which the trustee sale can be held after 21 days.  So the shortest period of time would be 111 days, but in practice it takes longer.  I suggest that you communicate with the lender to inform them that you are selling the property.  You will have to show them a purchase agreement or escrow instructions.